1. Field of Invention
This invention relates to a method and apparatus for the delivery and/or storage of one or more fluids and, in particular, to a method and apparatus for storing and delivering chemical and biological reagents.
2. Discussion of Related Art
The delivery of fluids plays an important role in fields such as chemistry, microbiology and biochemistry. These fluids may include liquids or gases and may provide reagents, solvents, reactants, or rinses to chemical or biological processes. Often, more than one fluid is delivered to a reaction vessel or site to promote interaction between the fluids or components of the fluids. Intermittent rinse fluids may also be used to remove unwanted reactants or to prepare a reactor, reaction site or assay site.
While various microfluidic devices and methods, such as microfluidic assays, can provide inexpensive, sensitive and accurate analytical platforms, fluid delivery to the platform can add a level of cost and sophistication that may require testing to be performed in a laboratory rather than in the field, where it may be most useful.
As chemical and biochemical platforms become smaller due to improvements in areas such as microfluidics, smaller reagent quantities are required to do a similar number of assays or reactions. Typically, however, smaller size platforms do not diminish the need to supply multiple reagents and rinses to a reaction site. For instance, some microfluidic assays may require less than a microliter of reagent fluids, but two, three or more different fluids may need to be supplied in accurate quantities and in proper sequence.
For microfluidic assays and reactors, fluids are often supplied by an operator using a micropipette. A fluid may be pipetted into an inlet of a microfluidic system and the fluid may be drawn through the system by application of a vacuum source to the outlet end of the microfluidic system. Reagents may also be pumped in, for instance by using different syringe pumps filled with the required reagents. After one fluid is pumped into the microfluidic device, a second can be pumped in by disconnecting a line from the first pump and connecting a line from a second pump. Alternatively, valving may be used to switch from one pumped fluid to another. Different pumps are used for each fluid to avoid cross contamination. This may be of particular relevance when two fluids contain components that may react with each other or, when mixed, can affect the results of an assay or reaction.
Continuous flow systems may use a series of two different fluids passing serially through a reaction channel. Fluids can be pumped into a channel in serial fashion by switching, through valving, the fluid source that is feeding the tube. The fluids constantly move through the system in sequence and are allowed to react in the channel. For example, a PCR reaction can be run using continuous flow. See Obeid et al., “Microfabrication Device for DNA and RNA Amplification by Continuous-Flow Polymerase Chain Reaction and Reverse Transcription-Polymerase Chain Reaction with Cycle Number Selection,” Analytical Chemistry, 2003, 75, 288-295.
The utility of fluid systems may be affected by the storage time, or shelf life, of any reagents that are to be used with a system. A portable microfluidic system can be transported to almost any location, but when reagents must be freshly prepared, the usefulness of the system in the field can be diminished. This may be true in particular for biological and biochemical based systems that may rely on reagents that, for example, are unstable, have short shelf lives or must be stored under special conditions, such as refrigeration.
An accurate early and ongoing determination of a disease condition is important for the prevention and treatment of human and animal diseases. One class of diagnostic techniques uses immunoassay reactions to detect the presence of either an antigen or an antibody in a sample taken from a subject. These immunoassay methods include, for example, ELISA, immunochromatographic assays (strip tests, dipstick assays and lateral flow assays), and sandwich assays. Accuracy, reliability, and ease of use of these types of assays has improved, but often testing requires laboratory conditions, power supplies, and training that may not be available in some areas where testing is desired.
One type of sandwich assay uses gold conjugated antibodies to enhance detection. For example, see PCT publication WO/91/01003. Enhancement of a gold colloid signal can be achieved by staining the gold colloids with silver. First, an antigen is immobilized onto a solid polystyrene substrate. A human anti-HIV antibody is then captured by the antigen and is therefore itself immobilized on the substrate. The antibody is then exposed to anti-human IgG labeled with a colloidal gold particle and thus labeled IgG becomes bonded to the antibody. The antigen-antibody-IgG complex is then exposed to a solution containing silver ions and these become nucleated around the gold particles as solid silver particles having a dark color to the eye.
The development of microfluidics and microfluidic techniques has provided improved chemical and biological research tools, including platforms for performing chemical reactions, combining and separating fluids, diluting samples, and generating gradients. For example, see U.S. Pat. No. 6,645,432, hereby incorporated by reference herein.